Medical injection device with electric motor drive control

ABSTRACT

This invention relates to an injection device for delivering a medicament to the human or animal body, in particular, but not exclusively, to a device having a replaceable medicament cartridge, including an auto-injector, wherein the injector device comprises: a housing; a piston rod for driving a bung of a medicament container; a drive mechanism including a motor for providing an output drive to the piston rod for delivering the medicament; and control means for controlling operation of the device.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/141,781 filed Oct. 22, 2011 which is a U.S. National PhaseApplication pursuant to 35 U.S.C. § 371 of International Application No.PCT/EP2009/067827 filed Dec. 23, 2009, which claims priority to EuropeanPatent Application No. 08022476.9 filed Dec. 27, 2008. The entiredisclosure contents of these applications are herewith incorporated byreference into the present application.

This invention relates to injection devices for delivering medicine tothe human or animal body and in particular, but not exclusively, todevices having a replaceable medicament cartridge, includingauto-injectors. Such devices are commonly used by those with diabetesfor the administration of insulin.

Medicament delivery devices are routinely used by persons without formalmedical training, i.e. patients where self-management of their conditionis increasingly common. These circumstances set a number of requirementsfor medicament delivery devices of this kind. The injector should berobust in construction, yet easy to use in terms of its operation by auser and the manipulation of the parts. In the case of those withdiabetes, many users will be of impaired vision and may also bephysically infirm. Devices that are too large of cumbersome maytherefore prove difficult to use, particularly someone with reduceddexterity.

Patent Specification U.S. Pat. No. 6,340,357 describes a drug deliverysystem in which the dose setting is read into an electronic circuit andthe dose setting movement of the dose setting elements relative to eachother is performed by an electromechanical device, e.g. a motorcontrolled by the electronic circuit in accordance with the read in dosesetting. The electronic control enables the apparatus to intervene byresetting a dose if a miss-handling of the device by the user isdetected during dose setting, such as opening of the cartridge holder.

Patent Specification WO 2007/094833 describes a metering system forautomatically adjusting for differential thermal expansion/contractionfor the efficient, accurate and reproducible metered delivery of fluids.The system allows the metering system drive to re-zero itself to producean accurate volumetric delivery of fluid from the dispensing container.

It is also known to detect a stall of the motor that drives the dosedelivery and to warn the user if a dose fails to be delivered. However,there remains a problem in the resetting of the device followingdetection of a motor stall event.

It is an aim of the present invention to provide a medication deliverydevice that alleviates this problem.

According to the present invention, there is provided an injectiondevice for delivering a medicament to a patient, wherein the injectordevice comprises: a housing; a piston rod for driving a bung of amedicament container; a drive mechanism including a motor for providingan output drive to the piston rod for delivering the medicament; andcontrol means for controlling operation of the device; characterised inthat:

the control means comprises: a drive signal generator for generating aninput drive signal for the motor; an encoder for generating an encoderoutput signal indicative of the output drive of the motor; and means forvarying the operational control of the device in dependence on acomparison between the input drive signal and the encoder output.

The input drive signal may be stepper pulses for driving the motor. Theencoder output signal may be a pulsed signal having a timingcharacteristic that corresponds to the output drive of the motor. Aplurality of reference points may be included in the device, eachreference point being indicative of a different operational aspect ofthe device, including any one or more of: backstop position; dosedelivered; door position; drive position; and reset threshold. Thereference points preferably relate to the input drive signal such thatrespective reference points correspond to respective counts of thestepper pulses with reference to a device datum. A comparison betweencounts of the pulsed encoder output with counts of the stepper pulsesmay be indicative of motor slip. In the event that motor slip or stallis detected the control means is operative for determining the quantumof slip relative to one of the reference points whereupon said varyingmeans adjusts the operational control of the device according to apredetermined criteria. The variation in operation control may be suchas to urge the device to a target operational state. For example, whenthe quantum exceeds a predetermined threshold value, the motor may bedeliberately stalled against a predetermined reference pointrepresentative of the target state. For example, the motor drive may bevaried so the state of the device is changed to a dose reset position ora ‘cartridge door open state’ for enabling replacement of the cartridge.Alternatively, the motor may be controlled such as to rewind the pistonrod to a backstop which defines a device datum or device reset position.

Embodiments of the present invention are advantageous in that theinjector automatically initiates a reset action when necessary andwithout needing user interaction. This leads to an improvement inbattery life and an avoidance or reduction in motor stall noise.

The invention will now be further described by way of example withreference to the accompanying drawings, in which like reference numeralsdesignate like elements:

FIG. 1 is a front view of an auto-injector that may include anembodiment of the present invention;

FIG. 2 is a front view of the auto-injector of FIG. 1 with a medicamentcartridge door shown in an open position for receiving a medicamentcartridge;

FIG. 3 is a perspective view of a motor for use in embodiments of thepresent invention;

FIG. 4 is a side view of the motor of FIG. 3 with an encoder;

FIG. 5a is a timing chart of motor drive and encoder output;

FIG. 5b is a timing chart of motor drive and encoder output showingmotor slip;

FIG. 6 is a flow chart illustrating a decision sequence that may beperformed by the control means; and

FIG. 7 is a functional block diagram of the control means.

In FIG. 1, an auto-injector 1 comprises a case 2 having a display 3 fordisplaying functional information relating to the operation of theauto-injector, including the set dose, number of doses remaining in themedicament cartridge. User interface buttons 4, 5 and 6 are provided toallow the user to operate the injector including priming, setting adose, opening a medicament cartridge holder and door 7, and activatingthe dispensing of the set dose. A threaded needle attachment 8 isprovided to which a needle can be attached for dose delivery andsubsequently removed and discarded. A cover (not shown) may be providedto fit over the lower portion of the case 2 to assist in protect thedevice from the ingress of particles and fluid. FIG. 2 shows theauto-injector 1 with the cartridge holder and door 7 in an open positionfor receiving a replacement medicament cartridge 9.

FIG. 3 shows a motor 13 within a drive mechanism (see FIG. 7). The motoris provided with a pair of flags 15 disposed at 180 degrees withreference to one another. An output gear 17 engages with a gear train(not shown) of the drive mechanism for driving the piston rod of theauto-injector 1. The motor 13 may be a stepping motor driven by a pulseddrive signal or stepper pulses illustrated schematically in FIGS. 5a and5b below. The pulsed drive signal is generated by an electronic controlcircuit within the control means. The control means will be described inmore detail with reference to FIGS. 5a to 7.

FIG. 4 is a side view of the motor 13 showing an optical encoder 19 inregistration with the flags 15. As the drive shaft of the motor 13rotates the flags 15, every edge of a flag causes a change in the outputof the optical encoder 19, so that the encoder outputs a series ofoutput pulses representative of the angular velocity of the drive shaft.The control means (microcontroller/microprocessor—not shown) detects andcounts these pulses. The encoder signal causes an interrupt in themicrocontroller/microprocessor. An interrupt causes an interruption ofthe current software program flow, executes a special interrupt softwareroutine and returns to the normal software flow after finishing theinterrupt routine. This technique is used to react immediately toexternal signals to make sure that every signal is recognized by themicroprocessor. In the embodiment shown in FIG. 4, a pair of flags 15 islocated at 180° and will therefore generate 4 pulses per motor turn. Oneencoder pulse is therefore equivalent to 5 motor pulses, assuming 20motor pulses for a single turn of the motor shaft.

FIG. 5a illustrates the relative timing between the motor drive orstepper pulses and the encoder output pulses during normal drivemechanism movement of the device. In this example, there are 5 motorstepper pulses to one encoder output pulse, the control means beingprogrammed to expect 5 motor stepper pulses to one encoder output pulse.Consequently, when 20 motor stepper pulses are counted at the same timethat the control means counts 4 encoder output pulses, the controlcomparison determines that the device is driving normally. That is,there is no motor slippage or no motor stall. FIG. 5a illustrates asituation where a count comparison between the encoder pulse output issuch as to indicate 15 motor stepper pulses whereas the actual count bythe control means corresponds to 19 or 20 pulses. In this case thecontrol means determines from the comparison that the motor movement hasencountered slippage. At this point, a subroutine is run by softwareprogrammed into the control means to make a determination as to thestate of the auto-injector in relation to predetermined reference pointsand a device datum position. The position of the piston rod when in afully retracted position may represent a backstop position or datumposition (i.e. “zero”) from which other device reference points may bereferenced. The datum position also corresponds to an absolute motorposition so that incremental movements relative to that correspond toother operational states of the device. These other device referencepoints are between zero and a maximum motor travel position through26858 motor stepper pulses. For example, from the datum position, amedicament cartridge 9 door latch open position may be represented by,for example, a motor position that corresponds to “datum position+4pulses”. A priming dose may be determined to have been effected bymovement of the motor 13 through 84 pulses from the backstop datumposition.

FIG. 6 shows an example of an administration routine that may be runwith the control means software during the administration of medicament.At 60, the user inputs via input buttons 4-6 a desire to start theadministration of a dose of medicament. The motor stepper and encoderpulse counts are examined at step 62 to determine if they differ fromone another by more than a predetermined amount. If YES, the controlmeans rewinds the drive mechanism until the motor stalls at thebackstop, at which point the device may be datumed or reset. The controlmeans software may then calculate the deficit in the medicamentadministered and perform means to administer this dose. If NO, theadministration continues until the dose is completely expelled.

FIG. 7 is a functional block diagram of the control means 70, to whichis connected a user input 72 corresponding to the user interface buttons4-6 of FIG. 1, and the drive mechanism 74. The control means 70 includesdial buttons 76 through which the user can dial the required dose and anLC display 78 for displaying the set dose. The control means softwaresets a dose value corresponding to that set by the user at 80 andconverts this into an appropriate pulse value for the stepper motor 13at 82. At 84, the software determines the current position of the motor13 by looking at the current pulse count of the stepper pulses generatedby the motor and determines a motor target position 86 in terms ofstepper pulses that corresponds to the reference point representative ofthe piston rod position that will deliver the dose set at 76/80. Thecontrol means software, motor control 88, generates the required stepperpulses to drive the motor 13 of the drive mechanism 74 and comparesencoder and motor pulses.

The invention claimed is:
 1. A controller for controlling operation ofan injection device for delivering a medicament, the controllercomprising: a drive signal generator that generates an input drivesignal for driving a motor, the input drive signal for driving the motorcomprising stepper pulses; and an encoder that generates an encoderoutput signal indicative of an output drive of the motor the encoderoutput signal being a pulsed signal having a timing characteristic thatcorresponds to the output drive of the motor, wherein the controllervaries the operational control of the device based, at least in part, ona comparison between the input drive signal and the encoder outputsignal, wherein a comparison between counts of the encoder output signalwith counts of the stepper pulses of the input drive signal provides anindication of a quantum of motor slip, wherein the motor is deliberatelystalled against a predetermined reference point when the quantum of slipexceeds a predetermined threshold value, and wherein the controllercalculates a deficit in the medicament administered that is a doseremaining to be administered and performs administration of the doseremaining to be administered.
 2. A controller according to claim 1,further comprising user interface buttons.
 3. A controller according toclaim 1, further comprising dose dial buttons.
 4. A method of deliveringa medicament to a patient using an injection device comprising ahousing; a piston rod for driving a bung of a replaceable medicamentcontainer, the piston rod retractable to a backstop position; a drivemechanism including a motor for providing an output drive to the pistonrod for delivering a user settable dose of the medicament and retractingthe piston rod to the backstop position; and a controller that controlsoperation of the injection device, the controller including a drivesignal generator that generates an input drive signal for driving themotor and an encoder that generates an encoder output signal indicativeof the output drive of the motor, wherein the input drive signal fordriving the motor comprises stepper pulses, wherein the encoder outputsignal is a pulsed signal having a timing characteristic thatcorresponds to the output drive of the motor, wherein the methodcomprises: starting administration of a dose of the medicament to apatient; determining, by the controller, a number of motor pulses and anumber of encoder pulses; varying the operational control of the devicebased, at least in part, on a comparison between the input drive signaland the encoder output signal including determining, by the controller,if counts of stepper pulses of the input drive signal and counts ofencoder pulses differ from one another by more than a predeterminedamount, wherein a comparison between counts of the encoder output signalwith the counts of the stepper pulses of the input drive signal providesan indication of a quantum of motor slip; stalling, by the controller,the motor against a predetermined reference point when the quantum ofslip exceeds a predetermined threshold value; calculating, by thecontroller, a deficit in the medicament administered that is a dose ofmedicament remaining to be administered; and performing administrationof the dose of medicament remaining to be administered.